1. Technical Field
The embodiments described herein relate to semiconductor memory device, and more particularly, to an auto-refresh control circuit and a semiconductor memory device using the same.
2. Related Art
Currently, a 2-rank DRAM device that operates as if two independent chips were built in one chip has been developed. The 2-rank DRAM device indicates a DRAM device that can operate as a single rank or two ranks. The 2-rank DRAM device can allow first and second ranks to operate cooperatively as a single rank or independently as two ranks by using two chip selection signals that are commands for selecting chips. Describing a 1 Gb DRAM for example, the 1 Gb DRAM is formed to have two ranks, and two chip selection signals are used to allow the two ranks to operate independently or cooperatively.
In the 2-rank DRAM device, when the first and second ranks operate cooperatively as a single rank, it is necessary for the first and second ranks to perform auto-refresh operation together. In addition, in the 2-rank DRAM, when the first and second ranks operate independently from each other, it is necessary for the first and second ranks to perform auto-refresh operation simultaneously or individually.